Icelandic architect Arnhildur Palmadottir has proposed creating buildings (and entire cities) out of lava. From her website:

Lava flow has shaped the landscape for billions of years, but in human times lava has been a destructive force. Basaltic lava flows can contain enough building materials for the foundations of an entire city that would rise in a few weeks. The Lavaforming project is a story of a world that has recognised that traditional building materials such as concrete and steel that have huge environmental impact are no longer usable to build the cities that are needed.

The basic idea is to create trenches and forms to direct the flow of the lava. Then just wait for the volcano to erupt and hopefully flow in the intended way.

More info: Surfaces Reporter

Update: Paul tells me that the Santa Maria Church in Randazzo, Sicily was built with black lava stones.
     Posted By: Alex - Sun Jul 31, 2022
     Category: Architecture

I've long wondered why you couldn't scoop up lava and pour it into molds to make blocks. It's my understanding (perhaps badly flawed) there are frequent lave flows in Hawaii which are reasonably accessible.
Posted by Phideaux on 07/31/22 at 03:17 PM
I suppose whether this would work depends a lot on the type of lava. On the one hand, you could get obsidian; on the other, basalt. Or even pumice. But I agree, it seems worth a try at least.
Posted by Richard Bos on 08/07/22 at 05:11 AM

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